DP Biology (first assessment 2025)

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Question 23M.2.SL.TZ2.6

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Date May 2023 Marks available [Maximum mark: 15] Reference code 23M.2.SL.TZ2.6
Level SL Paper 2 Time zone TZ2
Command term Describe, Explain, Outline Question number 6 Adapted from N/A
6.
[Maximum mark: 15]
23M.2.SL.TZ2.6

Between 1900 and 2020 the Earth’s average surface air temperature increased by about 1° C. Temperature affects many biological processes.

(a)

Explain how temperature affects enzymes.

[4]

Markscheme
  1. speed of reaction/catalysis increases as temperature rises;
  2. faster molecular motion so more collisions between substrate and active site;
  3. denaturation at higher temperatures;
  4. (denaturation causes) shape/conformation/structure of enzyme/active site altered/damaged;
  5. an enzyme works fastest at its optimum temperature;
  6. inactivation at lower temperatures (due to very few collisions);
  7. sketch graph to model the effect of temperature on enzyme activity;

Graphs would need to be well annotated.

Must not be bell shaped.

(b)

Outline the role of the thyroid gland in helping to control body temperature in humans.

[4]

Markscheme
  1. secretes thyroxin;
  2. thyroxin causes the metabolic rate to rise;
  3. heat released by metabolism;
  4. thyroxin increases generation of body heat;
  5. thyroxin stimulates shivering/stimulates brown adipose tissue (to release heat);
  6. more thyroxin secreted if body temperature too low/converse;

 

(c)

Describe how human activities have caused average surface air temperatures on Earth to increase.

[7]

Markscheme
  1. release of carbon dioxide;
  2. combustion of fossil fuels produces carbon dioxide;
  3. forest fires (caused by humans) produce carbon dioxide;
  4. deforestation reduces carbon dioxide uptake by photosynthesis;
  5. release of methane;
  6. from cattle/sheep/ruminant digestive systems / other verified source of anthropogenic methane;
  7. greenhouse effect / carbon dioxide/methane is a greenhouse gas;
  8. carbon dioxide/methane allow short wave radiation in sunlight to pass through the atmosphere;
  9. longer wave/infra-red radiation emitted by the warmed Earth’s surface;
  10. carbon dioxide/methane absorbs/reflects back longer wave/infra-red radiation;

 

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